In a common emitter (CE) amplifier having a voltage gain G, the transistor used has transconductance 0.03 mho and current gain 25. If the above transistor is replaced with another one with transconductance 0.02 mho and current gain 20, the voltage gain will be

Options

(a) 1.5 G
(b) 1/3 G
(c) 5/4 G
(d) 2/3 G

Correct Answer:

2/3 G

Explanation:

Voltage gain ∆ᵥ = β Rₒᵤₜ / Rᵢₙ
G = 25 Rₒᵤₜ / Rᵢₙ ….(i)
Transconductance gₘ = β / Rᵢₙ
Rᵢₙ = β / gₘ = 25 / 0.03
Puttin g this value of Rᵢₙ in eqn.(i)
G = 25 Rₒᵤₜ / 25 x 0.03 …(ii)
G’ = 20 Rₒᵤₜ / 20 x 0.02 …(iii)
From eqs. (ii) and (iii)
Voltage gain of new transistor G’ = 2/3 G